Determination of intrinsic second-order rate constant for acetophenone in reaction with hydroxyl radicals and its temperature-correction coefficients

Acetophenone is a refractory organic pollutant found in several industrial wastewaters. It can escape biological secondary treatment systems and cause adverse impacts on aquatic ecology. Further treatment through advanced oxidation processes, which generate powerful hydroxyl radicals, is a promising option. The intrinsic second order rate constant between acetophenone and hydroxyl radicals, as well as its temperature-correction coefficients, was determined using a homogeneous Fenton-like process at pH 2.5. Using the competitive kinetics technique with aniline as a reference compound, the intrinsic second-order rate constant for the reaction between acetophenone and hydroxyl radicals was determined to be 8.97×109 M−1s−1 at 25°C and 1 atm. This value remained consistent across various scenarios involving different reactant concentrations, hydraulic retention times, and operating modes. Hydroxyl radicals can reach a quasi-steady state during the initial stage of the batch operation. Using the quasi steady-state approximation and the initial rate technique, the previously unreported activation energy for the Arrhenius equation and the thermal coefficient for the Phelps empirical equation were determined to be 29 kJ/mol and 1.035, respectively, over the temperature range of 20–40°C. The concentrations of hydroxyl radicals at the quasi-steady state of the batch reactor and at the steady state of the continuous-stirred tank reactor were found to range from 5.0×10−14 and 1.1×10−13 M. This information is very beneficial for reactor design and operational monitoring of acetophenone removal by advanced oxidation processes.